BA 54 then BA 546 at Heathrow
Johannesburg → London → Bologna
Timetable, London time
06:55BA 54 from Johannesburg at the gate
19:25BA 546 to Bologna leaves the gate
12 h 30 apart on the timetable
BA 546 leaves 12 h 30 after BA 54 arrives on the timetable: more than half a day, so not a connection we count.